Kinetics of Manganese Oxidation by Cell-Free Extracts of Bacteria Isolated from Manganese Concretions from Soil

Abstract

A study of the kinetics of Mn 2+ oxidation catalyzed by cell extracts of two bacterial isolates (E 1 , Pseudomonas III [new isolate] and E 4 , Citrobacter freundii ) isolated from the core of manganese concretions from Greek soils is presented. The reaction velocity of Mn 2+ oxidation was determined from the rate of consumption of Mn 2+ . The oxidation of Mn 2+ was followed by measuring changes in Mn 2+ concentration by activation analysis and by atomic absorption spectrophotometry. The reaction velocity was directly proportional to cell extract concentration when the reaction time was 1 h. At longer reaction times, the relationship deviated from linearity because substrate concentration became limiting. The rate of Mn 2+ oxidation increased with the Mn 2+ concentration. Analysis of the results by application of the integrated Michaelis equation for determining Michaelis constants and maximal velocities either in the presence ( K m = 3.33 μmol/ml and V max = 1.25 μmol/ml·h) or in the absence of maleate buffer ( K m = 2.52 μmol/ml and V max = 2.04 μmol/ml·h) indicated a strong affinity between the oxidizing system and manganese. All results in this study are consistent with an enzymatic manganese-oxidizing system and give an indication of the mechanism of biological Mn 2+ oxidation in soil which differs from that in the marine environment.